The present invention relates to a high-speed evaporator defrost system for defrosting refrigeration coils of evaporators in a short period of time without having to increase compressor head pressure.
In refrigeration systems found in the food industry to refrigerate fresh and frozen foods, it is necessary to defrost the refrigeration coils of the evaporators periodically, as the refrigeration systems working below the freezing point of water are gradually covered by a layer of frost which reduces the efficiency of evaporators. The evaporators become clogged up by the build-up of ice thereon during the refrigeration cycle, whereby the passage of air maintaining the foodstuff refrigerated is obstructed. Exposing foodstuff to warm temperatures during long defrost cycles may have adverse effects on their freshness and quality.
One method known in the prior art for defrosting refrigeration coils uses an air defrost method wherein fans blow warm air against the clogged-up refrigeration coils while refrigerant supply is momentarily stopped from circulating through the coils. The resulting defrost cycles may last up to about 40 minutes, thereby possibly fouling the foodstuff.
In another known method, gas is taken from the top of the reservoir of refrigerant at a temperature ranging from 80xc2x0 F. to 90xc2x0 F. and is passed through the refrigeration coils, whereby the latent heat of the gas is used to defrost the refrigeration coils. This also results in a fairly lengthy defrost cycle.
U.S. Pat. No. 5,673,567, issued on Oct. 7, 1997 to the present inventor, discloses a system wherein hot gas from the compressor discharge line is fed to the refrigerant coil by a valve circuit and back into the liquid manifold to mix with the refrigerant liquid. This method of defrost usually takes about 12 minutes for defrosting evaporators associated with open display cases and about 22 minutes for defrosting frozen food enclosures. The compressors are affected by hot gas coming back through the suction header, thereby causing the compressors to overheat. Furthermore, the energy costs increases with the compressor head pressure increase.
U.S. Pat. No. 6,089,033, published on Jul. 18, 2000 to the present inventor, introduces an evaporator defrost system operating at high speed (e.g., 1 to 2 minutes for refrigerated display cases, 4 to 6 minutes for frozen food enclosures) comprising a defrost conduit circuit connected to the discharge line of the compressors and back to the suction header through an auxiliary reservoir capable of storing the entire refrigerant load of the refrigeration system. The auxiliary reservoir is at low pressure and is automatically flushed into the main reservoir when liquid refrigerant accumulates to a predetermined level. The pressure difference between the low pressure auxiliary reservoir and the typical high pressure of the discharge of the compressor creates a rapid flow of hot gas through the evaporator coils, thereby ensuring a quick defrost of the refrigeration coils. Furthermore, the suction header is fed with low-pressure gas to prevent the adverse effects of hot gas and high head pressure on the compressors.
It is a feature of the present invention to provide a high-speed defrost refrigeration system that operates a defrost of evaporators at low pressure.
It is a further feature of the present invention to provide a high-speed defrost refrigeration system having a compressor dedicated to defrost cycles.
It is a still further feature of the present invention to provide a high-speed defrost refrigeration system having a low-pressure defrost loop.
It is a still further feature of the present invention to provide a method for defrosting at high-speed refrigeration systems with low-pressure in the evaporators.
It is a still further feature of the present invention to provide a method for operating a high-speed defrost refrigeration system having a compressor dedicated to defrost cycles.
According to the above features, from a broad aspect, the present invention provides a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the compressing stage to the evaporator stage and adapted to receive a portion of the refrigerant in the high-pressure gas state. A first pressure reducing device on the first line reduces a pressure of the portion of the refrigerant in the high-pressure gas state to a second low-pressure gas state. Valves stop a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage and direct a flow of the refrigerant in the second low-pressure gas state to release heat to defrost the at least one evaporator and thereby change phase at least partially to a second low-pressure liquid state. A second line directs the refrigerant having released heat to at least one of the compressing stage and the condensing stage.
According to a further broad feature of the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a first compressor in a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage wherein the refrigerant in the high-pressure gas is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the compressing stage to the evaporator stage and is adapted to receive a portion of the refrigerant in the high-pressure gas state. Valves stop a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage and direct a flow of the portion of the refrigerant in the high-pressure gas state to release heat to defrost the at least one evaporator and thereby change phase to a second low-pressure liquid state. A dedicated compressor is adapted to receive an evaporated gas portion of the refrigerant in the second low-pressure liquid state. The dedicated compressor is connected to the condensing stage for directing a discharge thereof to the condensing stage.
According to a still further broad feature of the present invention, there is provided a method for defrosting evaporators of a refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The method comprises the steps of i) stopping a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage; ii) reducing a pressure of a portion of the refrigerant in the high-pressure gas state to a second low-pressure gas state; and iii) directing the portion of the refrigerant in the second low-pressure gas state to the at least one evaporator to release heat to defrost the at least one evaporator and thereby changing phase at least partially to a second low-pressure liquid state.
According to a still further broad feature of the present invention, there is provided a method for defrosting evaporators of a refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage having at least a first compressor, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The method comprises the steps of i) stopping a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator; ii) directing a portion of the refrigerant in the high-pressure gas state to the at least one evaporator to release heat to defrost the at least one evaporator and thereby changing phase at least partially to a second low-pressure liquid state; and iii) directing an evaporated gas portion of the refrigerant in the second low-pressure gas state to a dedicated compressor, the dedicated compressor being connected to the condensing stage for directing a discharge thereof to the condensing stage.
According to a still further broad feature of the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the compressing stage to the evaporator stage and adapted to receive a portion of the refrigerant in the high-pressure gas state. Valves are provided for stopping a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage and directing a flow of the refrigerant in the high-pressure gas state to release heat to defrost the at least one evaporator and thereby changing phase at least partially to a second low-pressure liquid state. A second line is provided for directing the refrigerant having released heat to the compressing stage, and pressure control means in the second line for controlling a pressure of the refrigerant reaching the compressing stage.
According to a still further broad feature of the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the compressing stage to the evaporator stage and adapted to receive a portion of the refrigerant in the high-pressure gas state. Valves are provided for stopping a flow of the refrigerant in the first low-pressure liquid state to at least two evaporators of the evaporator stage and directing a flow of the refrigerant in the high-pressure gas state to release heat to defrost the at least two evaporators and thereby changing phase at least partially to a second low-pressure liquid state. A second line is provided for directing the refrigerant having released heat in the at least two evaporators to the compressing stage. Temperature monitor means are adapted to monitor an average temperature of the refrigerant in the second line and to reverse an action of the valves when the temperature reaches a predetermined value to re-establish the flow of the refrigerant in the first low-pressure liquid state to the at least two evaporators of the evaporator stage.
According to a still further broad feature of the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded by an expansion valve to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the compressing stage to the expansion stage and adapted to receive a portion of the refrigerant in the high-pressure gas state. Valves are provided for stopping a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage and directing a flow of the refrigerant in the high-pressure gas state around the expansion valve to the at least one evaporator of the evaporator stage to release heat to defrost the at least one evaporator and thereby changing phase at least partially to a second low-pressure liquid state, to then be directed to the compressing stage.
According to a still further broad feature of the present invention, there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compressing stage having at least a first and a second compressor, wherein the refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein the refrigerant in the high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein the refrigerant in the high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein the refrigerant in the first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to the compressing stage. The defrost refrigeration system comprises a first line extending from the first compressor to the evaporator stage and adapted to receive at least a portion of discharged low-pressure refrigerant from the first compressor. Valves are provided for stopping a flow of the refrigerant in the first low-pressure liquid state to at least one evaporator of the evaporator stage and directing a flow of the discharged low-pressure refrigerant to release heat to defrost the at least one evaporator and thereby changing phase at least partially to a second low-pressure liquid state. A second line is provided for directing the refrigerant having released heat to the evaporator stage.